This invention relates to manually rotatable controls, and is particularly directed to a hand-rotated knob drive for rotating a shaft-driven device. The invention is more particularly concerned with a torque override mechanism in the knob drive that normally engages the knob and its associated drive stem, but effects disengagement if a predetermined maximum torque is exceeded.
The invention is favorably employed in the control handle of a cable actuated steerable probe such as an endoscope, borescope or guide tube, in which the steering knob is rotated clockwise or counter-clockwise to effect bending in one direction or the other in a bending plane.
With borescopes, endoscopes or guide tubes of this type, the users can apply excessive torque to the steering knob, or to both steering knobs in the case of a four-way steerable probe. If the bending neck of the probe is restricted against further articulation, tension in the associated steering cable can become high. This can cause damage such as cable stretch, or can pull off an associated cable terminator, or can damage the steering mechanism. If the steering is restricted because the probe's bending neck is lying against the wall of a body cavity, excess torque can result in tissue damage to the cavity wall or to an adjacent organ.
If the bending neck is not restricted, the steering mechanism encounters stops disposed on ends of toothed racks of the mechanism or elsewhere in the probe. If excessive torque is applied to the steering knobs after the stops are encountered, internal damage can result to the probe.